| Lake sediment is the source and the convergence of water pollutants, internal release of eutrophication and heavy metals pollution causes increasing attention especially after the effective control of outside pollutions. Average sulfate concentration in lakes keeps increasing sharply with the acid deposition, the acidic mining waste water emissions and containing sulfate fertilizer application, and the nutrient response to sulfate input is of great importance due to the inevitable relation between entrophication and ecological health. In this research, a six weeks experiment was conducted under indoor simulating condition with the samples from Lake Moshui in Wuhan, aiming to explore the influence of external sulfate on nitrogen, phosphorus and heavy metals transformation and the tending towards of sulfate, the main conclusions are as follows:(1) The input of external sulfate changed the physicochemical properties of overlying water and sediments of Lake Moshui. During the process of sulfate reduction, alkalinity was produced, and the pH became higher significantly, while the Eh showed opposite trend. Variation of pH decreased, and the time of the lowest of Eh cut short in the deeper sediments. pH and Eh showed a negative correlation on the whole. In later stage, changes of pH and Eh tended to be stable with the diminishing sulfate reduction.(2) The input of external sulfate promoted the proliferation of sulfate-reducing bacteria (SRB), and the SRB amounts decreased with increasing sediment depth. Sulfate was reduced to sulfide with intermediate valence as hydrogen sulfide, elemental sulfur, AVS and chromium reduction sulfur. AVS content in the sediments showed a trend of gradual decline, which was contrary to the variation in the contents of S0and chromium reduction sulfur. The upper layer sediment affected by sulfate was drastically. The decline of AVS content in S500was1/2.76to that in CK, while the rising contents of S0and chromium reduction sulfur were1.56and2.38times than CK. There was a negative correlation between AVS and chromium reduction sulfur, and the correlations for all sediment layers reached significant or extremely significant level. Sulfate reduction consumed the low-molecular-weight acid like acetic acid which was produced by some microbial activities such as anaerobic fermentation.(3) The release of nitrogen and phosphorus in the sediments was accelerated due to the sulfate reduction. The concentration of ammonia nitrogen increased gradually, while the release of phosphorus amount showed depressed trend. The concentration of SRP showed a trend of first rise then decrease with time. There was a negative correlation between SRP of the pore water and total phosphorus and inorganic phosphorus of the sediments, and the upper layer of the sediments reached extremely significant level. The concentration of SRP and sulfate of overlying water and pore water showed a negative correlation as well, and overlying water and upper layer of the pore water reached the significant and extremely significant level respectively.(4) Sulfate reduction promoted the decomposition of organic matter. The release of heavy metals, which determinated in situ by DET (Diffusive equilibrium in thin-films technique)/DGT (Diffusive gradients in thin-films technique), was affected by sulfate input. The amount of release was:Fe>Mn>Cu, and the deeper sediments showed smaller release amount of metals. The amount of Fe, Mn and Cu all showed a trend of first rise then decrease with the time. There was a significant positive correlation between SRP and Fe. The bioavailable concentration of Fe, Mn and Cu of the overlying water and the pore water of upper layer sediment in S00were low than CK in later stage, and the lower layer sediments had litter influence from external sulfate. |
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